Light waves may be made to carry information by modulating a light source, often a laser source, to change various properties of the light, such as its amplitude, phase, frequency, wavelength, etc. The light waves may be in the visible spectral band, the infrared spectral band, or another region of the electromagnetic spectrum. In some cases, an underlying signal, such as a radio frequency signal, may be modulated via amplitude, phase, or frequency modulation, or any combination thereof, and the light source may be modulated by the underlying signal. Optical receivers receive the light waves and measure properties or variations of the light wave, such as the amplitude, phase transitions, and the like, from which the underlying signal and the information may be recovered.
A receiver for line-of-sight communications using modulated light waves, such as a modulated laser beam, should collect signal from a large enough area that the acquired signal power is high enough for accurate detection. Conventionally a telescope may be aimed at the source laser and the cross sectional area of the telescope, or aperture, may determine how much signal power is collected and concentrated (e.g., focused) at a receiver. Some modulation schemes, such as phase modulation, for example, require coherent light, hence a laser is often the light source. When such light is collected and focused, the best reception occurs if all the light rays (across the cross-section of the telescope) arrive at the detector in unison as a single wavefront, maintaining alignment of the original phase relationships of the light rays. If some of the light rays have propagated through different media along the way, or were skewed, delayed, aberrated, or the like, as is typical for light waves traveling some distance through the atmosphere, wavefront correction may be required in conventional light-focusing systems. Such systems may use adaptive optics to attempt to correct the light rays to their original phase relationships and minimize the negative effect of aberration. In many cases, it may be impossible for conventional receivers to accurately demodulate aberrated light without wavefront correction.